Skip to main content ↑ ↓
Topic: Transmission Temp (Read 1902 times) previous topic - next topic

Transmission Temp

93 225 with 5.9 and 4 Speed (MT-643)
Weight: About 21,000 with a 3,000 toad

Just wondering about acceptable tranny temps. On our last trip we did lots of sustained steep climbing in first and second gear. The Cummins did fine and never got over 200 degrees. The trans temp, however, flirted with 300 (maybe 290 or 295). At that point I got worried and pulled over to let it cool down. The book says that normal for this trans is 160-220 and 300 is max. It recommends pulling over, revving to 1500 or so for several minutes until normal temp resumes. I'm wondering about real life experience with this setup (4 speed, no retarder).

I posted this over at rv.net and the responses indicated that I should absolutely change fluid and filter after having gotten this hot. The book seems to indicate otherwise. Thanks.
jor
93 225
95 300
97 270
99 320

Re: Transmission Temp

Reply #1 –
Jor,

Remember, you have Transynd in your transmission.  Should make a difference in allowable temperatures.  Never had a problem when we were in the mountains.  Will do some research and PM you if I find out anything.
We are only strangers until we meet; however, some of us are stranger than others

Re: Transmission Temp

Reply #2 –
A '93 U225 may not have had Transynd fluid in it when it was new.  Most likely it started life with Dexron as oem fluid.  My 1994 was switched over to Transynd by the orginal owner.  I changed it again when I purchased it last summer.  Transynd is the synthetic fluid that is OEM fluid in newer transmissions.  It extends you fluid change intervals from months to years!  Handles the heat very well.  Many with older transmissions have stayed with Dexron III, but I would change to the Transynd in a heartbeat!  Find a Allison lub shop and get it done, along with the filters. 

I just got back from Georgia.  Came up I-77.  Going up Fancy Gap, or anywhere else for that matter, the Transynd never hit 200 degrees!  In fact, it seldom went about 160.  When going up thru that area of the country, the ambiant tempuratures were not all that high.

On a side note - I was quite happy on how well the engine - transmission handled that hills.  Only had to drop into 3 gear a couple times.  That little 5.9 and 4 speed handled the hills very well.  Was somewhat surprised!!!  And averaged a bit over a solid 10 mpg.  My odometer and GPS compare quite well!!
1994 U225
build #4514

Re: Transmission Temp

Reply #3 –
As Jeff (previous owner of this rig) mentioned this tranny is running Transynd. Before this trip, the temp stayed around 150 to 200 or so but this time it was first and second gear for a long time and it started heating up. (real steep, lots of switchbacks) I figured an alarm would probably sound at 300 but it did not. I don't think there's anything wrong with the trans; just wondering about others' experience.
jor
93 225
95 300
97 270
99 320

Re: Transmission Temp

Reply #4 –
Did not know that you had Jeff's U225.  Those switchbacks sure would run it up.  Allison has some real good info on their web site, but you have to really dig for it.
1994 U225
build #4514

Re: Transmission Temp

Reply #5 –
I know I have hit 200 on Fancy gap in all three of my coaches. That is a big hill up and down but not too long. I find Cumberland Gap harder to keep the temps down. I will hit 205 easy on the up and down too.  That is by the silverleaf as well as the gauge. 
2025 Wanderbox Outpost 32 on F600 Expedition Motorhome
2015 Born Free Royal Splendor on Ford 550 nonslide version  for sale
Former Coaches  covering. 360,000 miles
1999 34 U270
2000 36 U320
2001 42' double slide U320
2018 Jeep Rubicon

Re: Transmission Temp

Reply #6 –
John, I have never noticed the tranny temps in my U-225 reaching those levels but I also never took it in the mountains or on grades that steep. Usually the transmission temp was a little lower than my engine temp. I do know that Jeff's engine temp gauge ran about 10 degrees cooler than mine did, but I always thought his was right and mine was wrong. I'd be very surprised to see the transmission temp that much higher than the engine temp. It may just be the gauge or sending unit. The transmission cooler is in the radiator on the 5.9.
The selected media item is not currently available.Kent Speers
Locust Grove, OK
1993 U300 SSE 40' (Restored at FOT 2009) Build 4323
720 watts Solar
6V92TA DDEC Silver Engine
2014 Subaru Outback

Re: Transmission Temp

Reply #7 –
Thanks for the tip on the trans cooler, Kent. (hard to track the hoses on this thing with that damn rear radiator!) I believe the gauge is accurate as in normal driving it stays around 150 or 160. It elevates a little on real long pulls as you describe. This trip really put it to the test with many recommended nte 20 or 25 mph turns and really steep and sustained grades up to over 8,000 altitude. I supposed I should mention (somewhat sheepishly)  that this particular mountain road was posted "Not recommended for trucks." I can't imagine taking it on anything tougher than that one.

I was pleasantly surprised at that 5.9; it just kept pullin'!
jor

93 225
95 300
97 270
99 320

Re: Transmission Temp

Reply #8 –
I do know that the synthetic lowered my temps by over 10 degrees on each of the roads I run all the time with grades. Then again I am 42 foot with a tag and run an ISM and hit the hill pretty hard to keep up my speed and try to run the same speed on the way down. Sometimes the grade lowers the speed limit for trucks to 35 MPH... Those are a bit harder to keep the tranny temp down.  I do but I have to watch it pretty closely and use the service brakes to slow my down every so often.  It takes a long time to cool down when you heat it up that much.  I also had an issue climbing out west a few years ago.  I was at altitude and it was 110 degrees out. It was pretty easy to get the engine temps up to 220 and I had to back off the throttle a bunch and slow way down to climb that hill...  Then again it was not steep but it went on and on for ever...
2025 Wanderbox Outpost 32 on F600 Expedition Motorhome
2015 Born Free Royal Splendor on Ford 550 nonslide version  for sale
Former Coaches  covering. 360,000 miles
1999 34 U270
2000 36 U320
2001 42' double slide U320
2018 Jeep Rubicon

Re: Transmission Temp

Reply #9 –
Quote from: jor –
Thanks for the tip on the trans cooler, Kent. (hard to track the hoses on this thing with that damn rear radiator!) I believe the gauge is accurate as in normal driving it stays around 150 or 160. It elevates a little on real long pulls as you describe. This trip really put it to the test with many recommended nte 20 or 25 mph turns and really steep and sustained grades up to over 8,000 altitude. I supposed I should mention (somewhat sheepishly)  that this particular mountain road was posted "Not recommended for trucks." I can't imagine taking it on anything tougher than that one.

I was pleasantly surprised at that 5.9; it just kept pullin'!
jor



John, if it was that steep going up I presume it was also steep going down. How did the PAC Brake handle the downhill. Did you have to use your chassis breaks very much? What gear did you run in?
The selected media item is not currently available.Kent Speers
Locust Grove, OK
1993 U300 SSE 40' (Restored at FOT 2009) Build 4323
720 watts Solar
6V92TA DDEC Silver Engine
2014 Subaru Outback

Re: Transmission Temp

Reply #10 –
Those are the times when the jake really shines.
The selected media item is not currently available. Dave Head & Megan Westbrook
Titusville, FL - The Great Outdoors
'98 270 buying this month
Toad is a 2018 F150 XLT

Re: Transmission Temp

Reply #11 –
Quote
It takes a long time to cool down when you heat it up that much.
Actually, it didn't take too long to cool down to normal temps, maybe three minutes or so. Just like the book says it should. Re engine temp, when I first got this rig, it was running hotter. The CAC was pretty obstructed but after I cleaned it off (lots of Simple Green and gingerly applied  pressure washer applications) the temps have dropped down considerably. I was really pleased with the Cummins staying cool on this tough uphill route.

Quote
How did the PAC Brake handle the downhill.
The exhaust brake was GREAT. I would start downhill at about 45 and in third gear. Every once in awhile, when it creeped up to 47 or so, I would stab the service brakes and bring it down to maybe 43. So, in third gear with the PAC on it would almost hold speed under 45. In fourth at higher speed, it doesn't do much. Haven't tried it in second yet. Anyhow, without the PAC I think I would have been white-knuckling it all the way down!

Also, I've been fooling around with different shift points on hills trying to figure the sweet spot for this little guy. So far, it seems to apply the most power at around 2150 revs or so. I hit a hill at a reasonable speed, keep pulling until the revs drop to right about 1500, drop it down to third right then. This pops the revs back up over 2000 and it continues to pull. I've found if I downshift too early, I lose ground. Having lots of fun figuring this thing out!
jor
93 225
95 300
97 270
99 320

Re: Transmission Temp

Reply #12 –
I agree on 2150 being the sweet point.

But
Horsepower:  160 - 215 HP @ 2,500 RPM 
Torque:  400 - 440 lb-ft @ 1,600 RPM

And somehow they are bumping ours upt to 230 HP.  And I know that they can get more out of that little engine. 
1994 U225
build #4514

Re: Transmission Temp

Reply #13 –
I feel the best speed for my 225 is 62mph but approaching a long steep hill I sometimes run it up to 70. That seems to be its happy spot. I also agree about down shifting  at 1500 rpms. The thing I like the most is the good mpgs. My U-300 gets 6.7 almost all of the time.
The selected media item is not currently available.Kent Speers
Locust Grove, OK
1993 U300 SSE 40' (Restored at FOT 2009) Build 4323
720 watts Solar
6V92TA DDEC Silver Engine
2014 Subaru Outback

Re: Transmission Temp

Reply #14 –
By the way, your CAC was replaced in 2007. I am very surprised it was all clogged up.
The selected media item is not currently available.Kent Speers
Locust Grove, OK
1993 U300 SSE 40' (Restored at FOT 2009) Build 4323
720 watts Solar
6V92TA DDEC Silver Engine
2014 Subaru Outback

Re: Transmission Temp

Reply #15 –
I was in third gear going down. It is a normal road for me to go west. I take I 68 thru thru the mountains in MD, PA, and WV to wheeling WV and then take 79 north to 70.  It is ok once you know how to drive it.  I hit aobut 70 to start unless I am blocked by other traffic and will hit the too 7 miles or so later at about 45 mph... Coming down the speed limit is reduced and trucks have a mandatory stop for a brake check too.
2025 Wanderbox Outpost 32 on F600 Expedition Motorhome
2015 Born Free Royal Splendor on Ford 550 nonslide version  for sale
Former Coaches  covering. 360,000 miles
1999 34 U270
2000 36 U320
2001 42' double slide U320
2018 Jeep Rubicon

Re: Transmission Temp

Reply #16 –
Re the economy, I'm really pleased. We are getting just south of 10 (9.67). This is about the same as my 96 3/4 ton Dodge pickup and two better than my 67 ford!

Quote
By the way, your CAC was replaced in 2007. I am very surprised it was all clogged up.
It was about 40% or so obstructed. At first I thought it was residue from the harmonic balancer explosion but then I moved to the engine heat-sound insulation theory. The original stuff was just disintegrating into a fine dust that would fall at the slightest jostle. I think it was that stuff mixed with oil or anti-freeze. Here's a photo of before and after.
jor



93 225
95 300
97 270
99 320

Re: Transmission Temp

Reply #17 –
Jor,
We have a U300 with a four speed. We only get transmission lockup starting midway in 2nd through 4th gear. The trans temp normally stays with the engine temp except when in the city (non-lockup) and on really steep grades in 1st and 2nd.  Above Taos, NM, we just  made the top of the grade at 10,500 feet in first gear. Narrow road with no place to cool off.  The transmission went to over 220 degrees  but cooled quickly on the way down. On long highway grades in the summer, the engine temp requires a lower gear long before the transmission gets warm.

Our driveway is 800 feet uphill with the first 300 very steep. When we brought the U300 home the first time, we had to crawl up the first 300 feet with the transmission temp going from 160 to 220 in the very short distance. After that, I just backed in the quarter mile and then did the steep part in reverse using just a little throttle and no drama.

My worry would be that 300 degrees for an extended period could damage internal seals regardless of the type of transmission fluid. Good to keep it idling to avoid "heat soak" when stopping for a couple of minutes to cool down.

Your 5.9 is a great engine. Overkill for pickup trucks.

Good luck,

Pierce & Gaylie
93' U300/36
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)
 

Re: Transmission Temp

Reply #18 –
Quote
My worry would be that 300 degrees for an extended period could damage internal seals...
Thanks, Pierce. I'm not worried as it didn't reach 300 and when it was getting close I pulled over and it immediately cooled to normal. Great idea backing up the driveway!
jor
93 225
95 300
97 270
99 320